1. Field of the Invention
This invention relates to a three-axis fiber-optic interferometer for carrying out detections along three axes and preferably along three orthogonal axes. This device thus performs a measurement of the three components along three axes, of a disturbance which has an unknown direction and which is liable to affect the propagation of a light beam.
2. Description of the Prior Art
An interferometer of the prior art mainly comprises a light-energy source usually consisting of a laser, an optical device composed either of a certain number of mirrors or of a fiber wound in a flat coil and forming a waveguide, a light-splitting and mixing device and a device for detecting and processing the detected signal.
It is known that, in these interferometers, there exist two waves which emerge from the light-splitting devices and travel in opposite directions on the same optical path.
A basic property of ring interferometers is that of reciprocity which can be expressed as follows: any disturbance of the optical path affects both waves in a similar manner despite the fact that these two waves are not subjected to this disturbance in the same direction.
There are, however, two types of disturbances which affect reciprocity.
In one of these two types, the disturbances vary in time over a period which is comparable with the time taken by the waves to propagate along the optical path of the interferometer. The other type consists of the so-called "nonreciprocal" disturbances which produce different effects on the waves, depending on whether they propagate either in one direction or in another along the optical path. The effects considered are physical effects which destroy the symmetry of the medium in which the waves propagate.
Two known effects are subject to the second type of disturbance:
the Faraday effect or colinear magnetooptic effect whereby a magnetic field produces a preferential electron spin orientation in an optical material;
the Sagnac effect or relativistic inertial effect in which rotation of the interferometer with respect to the inertial space destroy the symmetry of the propagation time. This effect is profitably employed in the construction of gyrometers in particular.
Should there be no occurrence of any "non-reciprocal" disturbances, the difference in phase between the two waves which recombine in the light-splitting and mixing device after traveling along the optical path is zero. The detecting and processing device detects signals representing the optical power of the composite wave obtained after recombination.
When the direction of the disturbance to be measured is not known, in order to measure the value of this disturbance and to determine its direction, it is necessary in accordance with the prior art to carry out measurements in a number of directions or else to employ a number of interferometers.
The interferometer in accordance with the invention differs from the prior art in that it makes provision for series multiplexing of three different axes in a fiber interferometer which makes use of only one source, a single detector and a single integrated optical circuit comprising a Y-junction, a phase modulator and a polarizer. This design concept clearly permits a reduction of the electric connection system and thus results in a more compact assembly.